In populations with limited genotyping, single-step genomic best linear unbiased predictions (ssGBLUP) can produce biased or less accurate genomic predictions due to incompatibilities between genomic and pedigree relationship matrices. The study evaluated the impact of five alternative ssGBLUP models for genomic predictions of milk, fat, and protein yield production traits in South African Holstein cattle. The dataset included 696,413 milk production records and pedigrees of 541,325 animals. Production traits were 305-day lactation yields for milk, protein, and fat. Genotype data were based on the Illumina 50K chip v3, with 53,218 SNPs. A total of 1221 animals with genotypes and 41,407 SNP markers were in the final dataset. The five models used to estimate genomic estimated breeding values (GEBVs) were the single-step method (ssGBLUP), ssGBLUP accounting for inbreeding (ssGBLUP_Fx), ssGBLUP with unknown parent groups (ssGBLUP_upg), and two ssGBLUP models with blending, tuning, and scaling parameters set to optimum values in constructing the inverse of the unified relationship matrix (ssGBLUP_adjusted). Realized prediction accuracies were highest for ssGBLUP_adjusted models (6-7% improvements compared to ssGBLUP). Accuracy of GEBVs for milk, protein, and fat yields ranged from 0.23, 0.29, and 0.30 for both ssGBLUP and ssGBLUP_Fx, 0.26, 0.32, and 0.34 for ssGBLUP_upg, and 0.29, 0.35, and 0.37 for ssGBLUP_adjusted models, respectively. Corresponding bias, expressed as regression coefficients, ranged from 0.30, 0.31, and 0.36 for ssGBLUP; 0.31, 0.32, and 0.37 for ssGBLUP_Fx; 0.41, 0.44, and 0.49 for ssGBLUP_upg; and 0.44, 0.47, and 0.53 for ssGBLUP_adjusted models, respectively. The improved accuracy and reduced bias observed with the ssGBLUP_adjusted underscores the importance of optimizing the blending of pedigree- and genome-based relationships to achieve more reliable GEBVs, thereby improving selection decisions in Holstein dairy cattle.

Wet carcass syndrome (WCS), a condition that negatively affects the quality of carcasses after slaughter, is seriously threatening the South African sheep industry. Despite its economic impact, the underlying genetic mechanisms of WCS remain unknown. Initially, WCS was predominantly observed in Dorper sheep, leading to speculation that the condition was breed-specific. However, recent reports indicate WCS has occurred in various sheep breeds. This study aimed to determine whether WCS is breed-specific and whether breed composition influences its incidence. Meat samples from 164 WCS-affected and 83 unaffected sheep were collected and genotyped using the Ovine 50K SNP Bead Chip. Principal Component Analysis (PCA) and ancestry matrix assessments revealed that WCS-affected and unaffected sheep belonged to different commercial breeds. Additionally, crossbred animals were affected. These findings suggest that WCS is strongly associated with breed and that Dorper and Merino-types show heightened susceptibility. The genetic diversity of the affected animals suggests a multifactorial etiology, potentially involving environmental and managerial factors. Future studies should also explore the physiological mechanisms underlying WCS, including metabolic and stress-related pathways, to develop effective prevention strategies.

The objective of this study was to evaluate the impact of blending, tuning, and scaling adjustments in ssGBLUP on the accuracy of genomic estimated breeding values (GEBVs) for South African Holstein cattle. The edited dataset included pedigree information for 541,325 animals, 696,413 phenotypic records (milk, protein, and fat yields), and genotypes for 1221 Holstein cattle. The accuracy of GEBVs was evaluated based on different parameter settings for blending (β = 0.05, 0.10, 0.20, 0.30, and 0.40), tuning (τ), and scaling (τ and ω), ranging from 0.60 to 1.00. The results show that ssGBLUP outperformed the traditional pedigree-based approach (ABLUP), with realized accuracies increasing from 0.01 to 0.23 for milk yield, 0.03 to 0.29 for protein yield, and 0.03 to 0.30 for fat yield. Blending with β = 0.30–0.40 slightly increased the accuracy, while tuning adjustments showed limited influence on the prediction results. Scaling factors had a significant influence on accuracy, with ω = 0.60 yielding the highest values (0.26 for milk, 0.32 for protein, and 0.34 for fat). The results of this study show the importance of optimizing the integration of pedigree and genomic information in ssGBLUP to improve the accuracy of genomic predictions, ultimately enhancing selection decisions and genetic progress in South African Holstein cattle.

The Afrikaner breed of cattle is indigenous to South Africa and, due to their hardiness, was once the most popular breed amongst South African farmers, although in recent years their numbers have decreased. The goal of this study was to assess factors affecting length of productive life, defined as the interval between production of the first and last calf, in Afrikaner cattle using survival analysis. The data spanned 40 years with an observed measure of length of life for 29,379 cows from 374 herds. Relative to similar analyses, few (n = 2964; 8.4%) cows had records that were right censored. The median length of productive life of an Afrikaner cow was just less than 6 years. Cows that were younger at their first parturition had longer productive lives than those that were older at their first calving. Cows that were born in the period from December to February had shorter productive lives than those born between March and November. The estimated animal genetic variance of 0.266 resulted in a heritability estimate for length of productive life in Afrikaner cattle of 0.225. Thus, there appeared to be sufficient additive genetic variance in Afrikaner cattle to enable genetic improvement in their length of productive life.

The objective of this study was to evaluate differences in the performance of offspring of boars selected with an index emphasizing resilience and boars selected based on a traditional index, emphasizing feed efficiency and carcass quality (traditional) index vs. a customized (resilience) index. The resilience index was identical to the traditional index, except that extra emphasis was placed on piglet vitality (increased by 66%), growth rate (decreased by 14%), and feed intake (increased substantially by 5,157%). Sows were mated to either boars selected based on the resilience index or boars selected on the traditional index. Weaned offspring were vaccinated for Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) and experimentally infected with PRRSV RFLP 1-7-4 four weeks later. Offspring were allocated to pens (n similar to 27 pigs/pen; n = 27 pens/group) by sire-selection group for a total of 1,458 pigs in 54 pens. The weight of each pen was recorded on 0, 42, and 110 d postinfection (DPI) and used to calculate average daily gain (ADG), average daily feed intake (ADFI), and feed conversion ratio (FCR). Mortalities were recorded from 0 to 110 DPI and necropsies were routinely performed to characterize pathogens present within the barn. Pigs classified as full value (i.e., >104 kg and void of defects) were slaughtered and hot carcass weight (HCW), backfat, loin depth, and lean weight were obtained from the slaughter plant. Effects of progeny group on performance, carcass characteristics, and mortality rate were estimated with a mixed linear model. Differences between progeny groups in ADG (P > 0.27), HCW (P = 0.68), backfat (P = 0.13), or loin depth (P = 0.39), and mortality rate (P = 0.29) were not detected. From 0 to 42 DPI, offspring of boars selected based on the resilience index had higher ADFI (0.06 kg/d, P = 0.01) and higher FCR (0.12, P = 0.01). In summary, results from this study do not support selection of boars for increased feed intake, piglet viability, and robustness in order to prevent losses caused by PRRSV, but selection response was only measured after one generation of male selection. The impact of multiple generations of selection, or the development of an index including traits derived from data collected under disease-challenged conditions should be explored. The data collected for this study are a valuable resource to explore additional genetic selection strategies for enhanced resilience to a multifactorial PRRS challenge.

Gastrointestinal parasite resistance is a heritable trait important to breeders of hair sheep. However, the U.S. Maternal Hair Index, provided by the National Sheep Improvement Program, omits parasite resistance. Selection indexes were designed in this study to continue improving total weight of lamb weaned per ewe lambing (TW), the current goal, and reduce postweaning fecal egg count (PFEC), an indicator of parasite resistance. These indexes placed varying emphasis on PFEC relative to TW. Annual genetic gains in TW and PFEC were predicted. Measurements for the traits used to construct the indexes were simulated to compare selection decisions-the number of rams and ewes chosen in common-between the current and the alternative indexes. Placing 79% of the selection emphasis on TW, and thereby 21% on PFEC, appeared preferable. With this balance, genetic gains in TW were reduced by only 2% relative to the current index, while PFEC was reduced favorably by as much as 8%. Additionally, over 60% of the males and 80% of the females were chosen in common between the current index and the proposed index including PFEC. Parasite resistance, therefore, can be incorporated as another selection criterion, with a positive impact on the productivity and fitness of hair sheep.

•Infusion of Bonsmara into Afrikaner immediately increased length of life.•Effects of infusion of Bonsmara into Afrikaner dissipated as backcrossing progressed.•Alternative strategies may be needed to increase length of life.

Objectives of this research were to examine differential gene expression profiles of Nguni and Bonsmara cattle fed diets differing in their energy density. The ultimate goal was to improve understanding of the mechanisms that underlie differences between these breeds and the potential interactions of the differences between breeds with the nutritive environment. The experiment was designed as a 2 × 2 factorial arrangement of breed and diet (12.5 MJ/kg DM vs. 10.9 MJ/kg DM). The initial feeding trial had 10 bull calves per treatment. However, financial constraints limited RNA sequencing to six animals per treatment and the RNA generated from one animal was of insufficient quality to be useful. Transcripts with false discovery rate P-values <0.05 and fold-changes >2.0 were considered significant. Bonsmara had a faster growth rate, heavier live and carcass weights, and better feed conversion compared to Nguni. However, lower levels of fat were observed in Nguni. Twenty different genes were differentially expressed, with three exhibiting interaction effects and all 20 having differences in transcript abundance between the breeds. A dietary effect was only observed for the one gene and that gene was also subject to an interaction effect with breed. Observed differences in gene expression between Bonsmara and Nguni by several genes affecting the structure or function of the mitochondria imply differences in energy metabolism between the breeds. Interaction effects on the abundance of some gene transcripts indicate the need to consider the diet when evaluating breed differences and conversely, consider breed when evaluating diets.

The increasing incidence of bovine congestive heart failure (BCHF) in feedlot cattle poses a significant challenge to the beef industry from economic loss, reduced performance, and reduced animal welfare attributed to cardiac insufficiency. Changes to cardiac morphology as well as abnormal pulmonary arterial pressure (PAP) in cattle of mostly Angus ancestry have been recently characterized. However, congestive heart failure affecting cattle late in the feeding period has been an increasing problem and tools are needed for the industry to address the rate of mortality in the feedlot for multiple breeds. At harvest, a population of 32,763 commercial fed cattle were phenotyped for cardiac morphology with associated production data collected from feedlot processing to harvest at a single feedlot and packing plant in the Pacific Northwest. A sub-population of 5,001 individuals were selected for low-pass genotyping to estimate variance components and genetic correlations between heart score and the production traits observed during the feeding period. At harvest, the incidence of a heart score of 4 or 5 in this population was approximately 4.14%, indicating a significant proportion of feeder cattle are at risk of cardiac mortality before harvest. Heart scores were also significantly and positively correlated with the percentage Angus ancestry observed by genomic breed percentage analysis. The heritability of heart score measured as a binary (scores 1 and 2 = 0, scores 4 and 5 = 1) trait was 0.356 in this population, which indicates development of a selection tool to reduce the risk of congestive heart failure as an EPD (expected progeny difference) is feasible. Genetic correlations of heart score with growth traits and feed intake were moderate and positive (0.289-0.460). Genetic correlations between heart score and backfat and marbling score were -0.120 and -0.108, respectively. Significant genetic correlation to traits of high economic importance in existing selection indexes explain the increased rate of congestive heart failure observed over time. These results indicate potential to implement heart score observed at harvest as a phenotype under selection in genetic evaluation in order to reduce feedlot mortality due to cardiac insufficiency and improve overall cardiopulmonary health in feeder cattle.

The Afrikaner breed of cattle is indigenous to South Africa and due their hardiness has been used in forming several new composite breeds. In the 1980 ' s, Afrikaner breeders became concerned about a perceived loss in fertility and the lack of attention to performance traits. The "infusion project" was developed to target short-comings of the Afrikaner breed with the introgression of Bonsmara alleles into Afrikaner cattle. However, documented evidence of resulting changes in the fitness of Afrikaner cattle is scant. A survival analysis of the infusion project's impact on longevity has been completed with the Cox model. The first backcross generation (BC1) and the initial Afrikaner-Bonsmara cross generation (F1) had the lower risk ratios at 0.815 and 0.837, respectively, when compared to the purebred Afrikaner indicating their greater longevity. The second (BC2) backcross generation did not differ in longevity relative to the purebreds (P >= 0.05). The infusion of Bonsmara impacted longevity in the short-term, possibly due to increased retained heterosis or the breed substitution effect. However, the effect on longevity diminished as the generations of backcrossing to Afrikaner progressed.

Estimated breeding values (EBV) for fecal egg counts (FEC) at 42–90 days of age (WFEC) and 91–150 days of age (PFEC) for 84 progeny-tested Katahdin sires were used to identify associations of deregressed EBV with single-nucleotide polymorphisms (SNP) using 388,000 SNP with minor-allele frequencies ≥0.10 on an Illumina high-density ovine array. Associations between markers and FEC EBV were initially quantified by single-SNP linear regression. Effects of linkage disequilibrium (LD) were minimized by assigning SNP to 2,535 consecutive 1-Mb bins and focusing on the effect of the most significant SNP in each bin. Bonferroni correction was used to define bin-based (BB) genome- and chromosome-wide significance. Six bins on chromosome 5 achieved BB genome-wide significance for PFEC EBV, and three of those SNP achieved chromosome-wide significance after Bonferroni correction based on the 14,530 total SNP on chromosome 5. These bins were nested within 12 consecutive bins between 59 and 71 Mb on chromosome 5 that reached BB chromosome-wide significance. The largest SNP effects were at 63, 67, and 70 Mb, with LD among these SNP of r2 ≤ 0.2. Regional heritability mapping (RHM) was then used to evaluate the ability of different genomic regions to account for additive variance in FEC EBV. Chromosome-level RHM indicated that one 500-SNP window between 65.9 and 69.9 Mb accounted for significant variation in PFEC EBV. Five additional 500-SNP windows between 59.3 and 71.6 Mb reached suggestive (p < 0.10) significance for PFEC EBV. Although previous studies rarely identified markers for parasite resistance on chromosome 5, the IL12B gene at 68.5 Mb codes for the p40 subunit of both interleukins 12 and 23. Other immunoregulatory genes are also located in this region of chromosome 5, providing opportunity for additive or associative effects.

Information on body weight and average daily gain (ADG) of growing animals is key not only to monitoring performance, but also for use in genetic evaluations in the pursuit of achieving sustainable genetic gain. Accurate calculation of ADG, however, requires serial measures of body weight over at least 70 days. This can be resource intensive and thus alternative approaches to predicting individual animal ADG warrant investigation. One such approach is the use of continuously collected individual animal partial body weights. The objective of the present study was to determine the utility of partial body weights in predicting both body weight and ADG; a secondary objective was to deduce the appropriate length of test to determine ADG from partial body weight records. The dataset used consisted of partial body weights, predicted body weights and recorded body weights recorded for 8,972 growing cattle from a range of different breed types in 35 contemporary groups. The relationships among partial body weight, predicted body weight and recorded body weight at the beginning and end of the performance test were determined and calculated ADG per animal from each body weight measure were also compared. On average, partial body weight explained 90.7 +/- 2.0% of the variation in recorded body weight at the beginning of the postweaning gain test and 87.9 +/- 2.9% of the variation in recorded body weight at its end. The GrowSafe proprietary algorithm to predict body weight from the partial body weight strengthened these coefficients of determination to 95.1 +/- 0.9% and 94.9 +/- 0.8%, respectively. The ADG calculated from the partial body weight or from the predicted body weight were very strongly correlated (r = 0.95); correlations between these ADG values with those calculated from the recorded body weights were weaker at 0.81 and 0.78, respectively. For some applications, ADG may be measured with sufficient accuracy with a test period of 50 days using partial body weights. The intended inference space is to individual trials which have been represented in this study by contemporary groups of growing cattle from different genotypes.

The objective of this study was to evaluate the effects of various data structures on the genetic evaluation for the binary phenotype of reproductive success. The data were simulated based on an existing pedigree and an underlying fertility phenotype with a heritability of 0.10. A data set of complete observations was generated for all cows. This data set was then modified mimicking the culling of cows when they first failed to reproduce, cows having a missing observation at either their second or fifth opportunity to reproduce as if they had been selected as donors for embryo transfer, and censoring records following the sixth opportunity to reproduce as in a cull-for-age strategy. The data were analyzed using a third-order polynomial random regression model. The EBV of interest for each animal was the sum of the age-specific EBV over the first 10 observations (reproductive success at ages 2-11). Thus, the EBV might be interpreted as the genetic expectation of number of calves produced when a female is given 10 opportunities to calve. Culling open cows resulted in the EBV for 3-yr-old cows being reduced from 8.27 ± 0.03 when open cows were retained to 7.60 ± 0.02 when they were culled. The magnitude of this effect decreased as cows grew older when they first failed to reproduce and were subsequently culled. Cows that did not fail over the 11 yr of simulated data had an EBV of 9.43 ± 0.01 and 9.35 ± 0.01 based on analyses of the complete data and the data in which cows that failed to reproduce were culled, respectively. Cows that had a missing observation for their second record had a significantly reduced EBV, but the corresponding effect at the fifth record was negligible. The current study illustrates that culling and management decisions, and particularly those that affect the beginning of the trajectory of sustained reproductive success, can influence both the magnitude and accuracy of resulting EBV.

The objective was to develop selection indexes for Nellore cattle raised in full-cycle production system in the Brazilian Pantanal. The resulting offspring are retained as replacements or sold at two years of age. Preliminary analyses explored effects of scale on economic values (EV). However, given the available data, these effects were very small. Presented herein are results from a simulated system consisting of 5,000 cows with all animals maintained on pasture as is typical in Pantanal. The EV were determined by approximating the partial derivatives of the profit function, changing one trait at a time, by one unit, while keeping the other traits constant. Traits in the breeding objective were mature cow weight, direct and maternal weaning weight, postweaning average daily gain, subcutaneous fat depth, longissimus muscle area, and stayability. Economic values were calculated on the basis of number of animals (per head), number of animal units, and arroba of carcasss weight. Regardless of the basis, maternal weaning weight and subcutaneous fat depth made negligible contributions to the breeding objective. Proportions of variation in the breeding objectives (per head, per animal unit, per arroba) explained by cow weight, direct weaning weight, postweaning average daily gain, stayability, and longissimus muscle area were: 13, 13, 17; 6, 1, 5; 3, 3, 4; 67, 67, 61; and 11, 17, 13, respectively. These indexes may aid Nellore breeders in their selection decisions, thus facilitating the genetic progress and increased productivity and profitability of Pantanal herds.

Ultrasound technology provides cattle breeders with a quick, noninvasive, and inexpensive way to measure carcass data on live animals. Ultrasound data are used as indicator traits in cattle genetic evaluations for economically relevant carcass traits. Ultrasound cattle genetic evaluations assume homogeneous additive genetic and residual variance. Thus, the objective was to partition phenotypic variance in ultrasound carcass measurements into components for additive genetic effects, technicians, contemporary groups within technicians, and residual and to examine the homogeneity of these variances among image interpretation laboratories. Records of longissimus muscle area (LMA), percentage of intramuscular fat (IMF), and subcutaneous fat depth (SFD), measured using ultrasound, were provided by the American Angus Association (n = 65,967), American Hereford Association (n = 43,182), and American Simmental Association (n = 48,298). The data also included contemporary group, technician, imaging lab, and a three-generation pedigree for each animal. Variance components for ultrasound carcass measurements were first estimated with univariate animal models for each breed and imaging laboratory using derivative-free restricted maximum likelihood. Then, treating data from each imaging laboratory as separate traits, genetic correlations between laboratories for LMA, percentage of IMF, and subcutaneous fat were estimated with trivariate animal models. The technician explained 12-27%, 5-23%, and 4-26% of the variance for IMF, SFD, and LMA, respectively, across all three breeds. Variance due to technician was often greater than variance due to additive genetic effects but almost always less than that explained by the contemporary group. Within breeds, estimates of additive genetic variance for LMA, SFD, and IMF differed (range divided by mean) among laboratories by 4.5%, 21.5%, and 39.4 % (Angus); 31.6%, 15.0%, and 49.1% (Hereford); and 19.9%, 46.6%, and 55.3% (Simmental), respectively. Likewise, estimates of residual variance for LMA, SFD, and IMF differed among laboratories by 43.4%, 22.9%, and 43.3% (Angus); 24.9%, 15.2%, and 79.2% (Hereford); and 26.4%, 32.5%, and 46.2% (Simmental), respectively. Genetic correlations between labs across breeds ranged from 0.79 to 0.95 for IMF, 0.26 to 0.94 for SFD, and 0.78 to 0.98 for LMA. The impact of the observed heterogeneity of variance between labs on genetic evaluation requires further study.

Two hundred seventeen grass-finished Braford steers were assessed by ultrasonic scanning and subsequently harvested with their pistol hindquarters fabricated into boneless wholesale cuts. The Longissimus thoracis muscle area and subcutaneous fat depths were measured. The objectives of this study were: 1) to develop prediction equations for weights of the pistol hindquarter and high-value commercial cuts, and 2) to estimate sample size needed for experiments comparing pistol hindquarter retail product weight using either physically or ultrasonically measured carcass traits. Carcass measurements explained 44 % to 94 % of the variation in weights of individual cuts, whereas, measurements that were made using ultrasound explained 42 % to 90 % of the variation in the weights. Models used to predict the weight of pistol hindquarter retail product with carcass measures and ultrasound measures showed high coefficient of determination (R 2 = 0.92 and 0.97, respectively). Whether based on carcass or ultrasound measures, models used to estimate weight percentage of fat trimmed from the pistol hindquarter had lack of fit. In general, models for individual cuts weights that used traits measured with ultrasound as independent variables approached the accuracy of models using carcass traits. Thus, only slightly greater samples sizes were required to have equivalent power to detect differences in retail product weights using ultrasound measures. For experiments of equivalent power, differences in the number of animals required may be offset by avoiding costs for slaughter and fabrication.

doi: 10.1093/af/vfaa017 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons. org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com © Grobler, de Witt, Cason, Einkamerer, Josling, O’Neill, Fair, Baloyi, MacNeil, Neser Feature Article Training the next generation of animal scientists for South Africa

The aim of this study was to develop selection indices for Nellore cattle raised in two complete cycle production systems in the Brazilian Cerrado, with Tropical climate, where bulls are mated with heifers and mature cows. The resulting offspring are retained as replacements or sold at 2 years. In System 1 (S1), the animals were raised and finished on pasture, while in System 2 (S2), the animals were raised on pasture and males were finished in the feedlot. The economic values were determined by stochastic simulation of the production system using partial derivatives of the profit function, changing one trait at a time, by 1 unit, while keeping the other traits constant. Relative economic values were calculated for cow weight at 5 years, weaning weight, maternal weaning weight, postweaning average daily gain, fat thickness, ribeye area, and stayability. The economic values were, respectively, US$0.67, US$0.41, US$-0.15, US$0.09, US$-0.17, US$187.6 and US$2.7 for S1, and US$0.47, US$0.45, US$-0.004, US$0.28, US$-0.59, US$157.5 and US$0.73 for S2. Consequently, increased profitability can be obtained by improving the cows' ability to stay in the herd, cow weight, ribeye area, weaning weight, and postweaning gain. The accuracy of the indices was 0.85 (S1) and 0.86 (S2). The application of these indices will aid Nellore breeders to select superior animals, facilitating the genetic progress and profit of the herd.

Hays Converter (HC), the first registered Canadian beef breed, was developed by Harry Hays in the 1950's as a composite with contributions from Holstein, Hereford, Brown Swiss and with a later introgression of Angus. The breed is well adapted to the Western Canadian climate. Calves reach market weight early, convert feed to gain efficiently, and have excellent carcass quality and yield. The edited data consisted of 21,612 weight records taken at ages 1 to 474 days, from 8,850 animals born at Red Bow Ranching Ltd., Calgary, Alberta between 1970 and 2016. This study aimed to evaluate the genetic parameters and trends in birth, weaning and yearling weights of HC through comparison of different multiple trait models (MTM) with a random regression model (RRM). In MTM scenarios, both adjusted and unadjusted data were examined besides considering contemporary groups (CG) as fixed or random. Estimates of variance components, heritability and genetic correlations from the two approaches were not substantially different and showed similar changes along the growth trajectory. Although there was a considerable reduction in genetic trends from 2004 to 2008, due to weak sire selection, trends generally increased through 2016. Overall, both models performed similarly and fixed CG were preferred.

This study evaluated associations of heat shock proteins (HSP) and an oxidative stress protein, protein deglycase (DJ1), with beef quality and tenderness. Samples from the longissimus thoracis (N = 99) were collected pre-rigor (day 0) and after 14-d aging. Warner-Bratzler shear force (WBSF), myofibrillar fragmentation index (MFI), and a trained sensory panel were used to determine meat quality. Protein abundance of DJ1 and 2 HSP—HSPβ1 and HSPA—were assessed. Regression analyses demonstrated that DJ1 abundance after 14 d of aging is a predictor of WBSF (P < 0.001), MFI (P = 0.02), and sensory panel tenderness (P < 0.001). Abundance of HSPβ1 after 14 d of aging is also a predictor of MFI (P = 0.03). Additionally, abundance of both HSPβ1 and DJ1 pre-rigor are predictors of juiciness (P < 0.05). Abundance of HSPβ1 pre-rigor was correlated with WBSF (R = 0.67), sensory panel tenderness (R = −0.44), juiciness (R = −0.30), and umami (R = −0.20). Abundance of DJ1 pre-rigor was also correlated with WBSF (R = 0.72), sensory panel tenderness (R = −0.44), juiciness (R = − 0.24), and umami (R = −0.31). After 14-d aging, HSP β 1 abundance was cor- related with WBSF (R = 0.66), sensory panel tenderness (R = −0.34), juiciness (R = −0.34), umami (R = −0.33), and brown/ roasted (R = −0.30). Abundance of DJ1 after 14-d aging was also correlated with WBSF (R = 0.68), sensory panel tenderness (R = −0.41), juiciness (R = −0.21), and umami (R = −0.28). These results demonstrate that abundance of HSPβ1 and DJ1 both pre-rigor and after 14 d of aging are correlated with meat tenderness and end-product quality as assessed by a trained sensory panel. Regression analyses further reveal that abundance of DJ1 and HSPβ1 after 14 d of aging is causative in development of beef tenderness and juiciness, respectively. Taken together, these results suggest that abundance of DJ1 is a predictor of tenderness, whereas abundance of HSPβ1 is related to meat quality but cannot be used to predict tenderness.